The drilling and completion of horizontal wells in recent years has offered dramatic improvements in the production of hydrocarbons and their recovery from the formations in which they are found. Although horizontal wells have been known for many years, it has only been in the last decade that this technology has been accepted by the industry and used as a proven and cost effective means to increase production and maximize ultimate recovery of hydrocarbons from a reservoir formation while lowering the cost to do so. As the industry has come to realize, horizontal wells frequently improve production by factors of 5 to 10 time in suitable reservoirs, such as for example those which are located in naturally fractured areas or are in heavy oil application zones.
Because of the improved economics in both the cost of production and the ultimate recovery of hydrocarbons reserves associated with horizontal drilling generally, many areas of the world have adopted such drilling techniques over the older technique of just drilling vertical wells. As horizontal and multilateral wells generally minimize the number of well locations and infrastructure required to develop an oil and gas field, this technique has become particularly important in high cost or environmentally sensitive areas, such as offshore locations, where reducing the number of platforms often results in significantly reduced investment and lower operational costs. Other areas for drilling which have adopted the use of laterals or multilateral which are particularly useful for horizontal development include reservoirs in urban areas, wildlife preserves, and permanent frost zones.
Multilateral wells are becoming increasingly important both from the standpoint of drilling a new well or for reworking an existing well to improve productivity and maximize the recovery of hydrocarbon reserves in place. Thus the use of multilateral wells have been accepted in reservoirs were horizontal drilling allows optimization of hydrocarbon recovery as for example in water drive systems which allow water injection efficiency to be increased and in the development of thin, or stacked reservoirs which would otherwise require many vertical wells, and in well as reservoirs with coning problems where by using horizontal drilling allows laterals to be optimally spaced for the fluid contact.
The incentives of cost effectiveness and environmental soundness, have expanded the use of multilateral or horizontal wells to be used in both the development of new wells and for re-entry of existing wells in established fields for stimulation and workover activities. Further the industry in its search for the most cost effective means to produce hydrocarbons with the least environmental impact has turned to multilateral and horizontal wells in great numbers.
The reasons are simple, as to why the industry has turned to multilateral wells, because in using multilateral wells drilled off a single main well bore, only one single main well bore is needed to be drilled and the additional recovery from the well is achieved by drilling laterals from the one single main well bore. However as the industry has placed ever increasing dependence on S0 multilateral well completion, there has been greater demand within the industry for advancing the technical capabilities of the multilateral technology. For example in completions systems and technology for the installation of lateral junctions in certain formations which are well known, there has been a primary barrier to the increased use of multilateral technology. This barrier has been the limitations in the completion options available, particularly in those situations in which a sealed junction is required to effectively produce a reservoir. Situations, such as those in which a hydraulically sealed lateral junction are desired, include unconsolidated or weakly consolidated formations, in order to avoid collapse of the junction, or in those junctions in which water injection is planned, or when the influx of formations fluids into the primary casing is unacceptable. These are just some of the situations which the current technology has not been able to over come on a consistent basis, except with the most expensive technologies in use today.
Further the technology which has only recently become available for the formation of junctions with hydraulic integrity is often too expensive to allow its utilization in all but the large budget wells, such as those found in offshore locations. At the present time, this sealed completion technology is generally not accepted as reliable by the industry for the average budget well. This has resulted in potentially high economic risk to install such systems. In addition, these completion systems may not allow the capability to selectively re-enter these laterals at a future time, nor to pressure test the junction for hydraulic integrity prior to the removal of the installation tools.
The prior art until the mid-1990's did not typically have a liner laid in a lateral and therefore these laterals were not tied back to the main well bore which severely limited or made impossible the re-entry of these laterals when workovers or cleanouts were required. However, subsequently, it became increasingly popular to case the laterals, as well as to tie back these laterals to the main well bore, but this tie back technology though making it easier to re-enter the well did not allow the junction to be hydraulically sealed to a significant pressure, such as 1,000 psi or more.
Also in the prior art where some sealing was able to be obtained it usually required multiple trips to install and perfect the seal, often 3 or more. This resulted in great expense in rig and personnel time, particularly in those high cost locations, such as offshore areas, which meant that many wells could not afford the technology and thus those wells could not receive the benefit of the multilateral technology.
Moreover, these earlier prior art systems did not allow the hydraulic integrity of the completed junction to be tested, and/or possibly repaired, prior to removing the tools used to install the seal. This was especially important in the high cost locations because of the excess expense in remobilization of the rig equipment and personnel for re-tripping back into the hole to bring the seal up to the design criteria determined necessary.
The prior art in many cases had to leave a packer in the main well bore in order to even attempt the re-entry back into the lateral well bore, which thus placed an obstruction or limit on the access to the main well bore below the packer. This forced well operators to have to make an election of which way they wanted to go and limited the number of lateral which could be drilled off on main well bore, if they elected to leave the packer in place in the main well bore.
Further, the prior art is legion with patents attempting to solve the problems of providing a reliable completion of a multilateral well such as U.S. Pat. No. 2,397,070 which describes a lateral well bore completion using flexible casing together with a movable gate for closing off the lateral. Of a similar nature is U.S. Pat. No. 2,797,893, which discloses a method for completing lateral wells using a flexible liner and a deflecting tool.
Several other prior patents such as U.S. Pat. No. 5,318,122 attempted to accomplish seals using a deformable device that selectively seals the juncture between the vertical and lateral wells using an inflatable mold which utilized a hardenable liquid to form a seal in conjunction with an expandable memory metal device or other devices for plastically deforming a sealing material to form a seal.
Such patents as U.S. Pat. No. 5,787,987 attempted to form a seal in the joint between the window in the well bore casing and the tubing being run into the lateral, by attempting to use the inside surface of the well bore casing as the sealing surface in conjunction with the flange being put into the well to seat with it. The sealing surface about the well bore casing does not provide as high of quality seal because of the material of the well bore casing not being a material which has been prepared for the purpose of forming a seal. Once in place then another run would be made into the well to put in place a sleeve to wedge the flange against the inside wall of the well bore about the window to form the seal. In this patent the old problem of multiple runs into a well to achieve a seal in the window section again shows up.
Further such art of a general nature including U.S. Pat. Nos. 2,452,920, 4,402,552, 5,289,876, 5,301,760, and U.S. Pat. No. 5,474,131 provided yet more examples of the teaching of the prior art which attempted to solve the problems in this art without the results which are achieved by the invention of this patent.